With the growing interest in energy conservation, increasingly more industrial work machines are supplied with electric drive assemblies or systems for driving the work machine and operating its various tools or functions. Ongoing developments in electric drives have made it possible for electrically driven work machines to effectively match or surpass the performance of mechanically driven work machines while requiring significantly less fuel and overall energy. As electric drives become increasingly more commonplace with respect to industrial work machines, and the like, the demands for more efficient generators and techniques for controlling same have also increased.
An electric motor of an electric drive machine is typically used to convert mechanical power received from a primary power source, such as a combustion engine, into electrical power for performing one or more operations of the work machine. Additionally, an electric motor may be used to convert electrical power stored within a common bus or storage device into mechanical power. Among the various types of electric motors available for use with an electric drive system, switched reluctance motors have received great interest for being robust, cost-effective, and overall, more efficient. While currently existing systems and methods for controlling switched reluctance motors provide adequate control, there is still room for improvement.
Typical control schemes for switched reluctance motors may involve operating two switches of each phase of the motor in one of two general operating modes, for example, single pulse and current regulation modes of operation. Single pulse modes are directed toward higher speed tasks requiring more power output, while current regulation modes are directed toward lower speed tasks requiring more torque output from a driven machine. Moreover, among typical current regulation modes, nominal speed tasks may be operated by hard chopping current to the two switches of each phase, while relatively lower speed tasks may be operated by soft chopping current to the two switches of each phase.
A hard chopping routine sources a pulsed phase current by simultaneously opening and closing both switches of each phase at the required frequency, whereas a soft chopping routine sources soft pulsed phase current by holding a first switch closed while opening and closing only a second switch at the required frequency. Soft chopping routines repeatedly subject significant thermal stress upon only one of the two switches in a phase leg. The added burden to such switches can result in premature failures in the associated power converter circuit. Such failures in the power converter circuit may in turn cause premature failures in the electric drive system and thus prevent work machines and other related tools to achieve initial performance requirements.
Accordingly, there is a need to improve the overall efficiency and functionality of an electric drive system. Moreover, there is a need to improve the switching routine or strategy associated with operating a switched reluctance motor during a motoring mode in high current, high load situations, such as at zero to low speeds. Furthermore, there is a need to more efficiently engage switches of a phase leg during soft chopping routines so as to prolong the life of the switches and of the overall electric drive system.